1. Field of the Invention
This invention relates to a master mask, a method which forms the master masks, an exposure method using the master masks, and a semiconductor device manufacturing method using the exposure method. More particularly, this invention relates to master masks used when a pattern of size larger than a region which can be exposed at one time is exposed on a to-be-exposed object, for example, when a reticle is formed, a method which forms the master masks, an exposure method which forms an IC chip pattern on a reticle by an exposure/transfer device by use of the master masks, a semiconductor device manufacturing method which forms a etching mask or a photoresist pattern by use of a reticle formed by the exposure method, and a semiconductor device manufacturing method using a photoresist patterned by the exposure method as a mask.
2. Description of the Related Art
The conventional exposure method which forms a pattern on a reticle by use of an exposure/transfer device is explained. As the exposure/transfer device, an i-line stepper is used. The i-line stepper reduces the pattern on the master mask to one fifth so as to transfer the reduced pattern onto the reticle with high precision. The size of a pattern which can be exposed at one time (which is hereinafter referred to as a shot) is a square form of 22 mm×22 mm on the reticle. Generally, a pattern on the reticle has the size of approximately 100 mm×100 mm. Therefore, when a desired pattern is formed on the reticle by use of the i-line stepper, it is necessary to couple a plurality of shots. There are two methods for coupling a plurality of shots.
The first method is to perform the exposure process while adjacent shots are simply put in contact with each other. The method is simple, but there occurs a possibility that the precision will be lowered in portions where shots are coupled.
The second method is to mount a special optical filter on the i-line stepper and perform the exposure process while portions of adjacent shots are arranged to overlap each other. In the present specification, the method is referred to as a “superposition exposure method” below. By use of the superposition exposure method, shots can be coupled with such high precision as to neglect coupled portions. The substantial size of the shot is 21 mm×21 mm when the above method is used.
One example of a pattern to be formed on the reticle is shown in FIG. 1A. All of the dimensions indicated in the present specification are expressed as the dimensions on the reticle. As shown in FIG. 1A, the repetition interval at which functional elements A, that is, IC chip patterns are arranged is 33 mm in the X direction and 30 mm in the Y direction. Then, 3×4=12 functional elements A in total are arranged on a reticle 101.
The functional elements A arranged on the reticle 101 is surrounded by a dicing region 102 with the width of 0.5 mm on the upper and lower sides and right and left sides and the whole size of a pattern to be formed on the reticle is 99.5 mm×120.5 mm. Like the functional element A, in the dicing region 102, a fine pattern is formed. The fine pattern is used as a quality control mark when a pattern drawn on the reticle 101 is exposed on the wafer and is different from that of the functional element A. All of the patterns formed in the functional elements A are the same patterns and have repetitiveness, but the above patterns do not basically have the repetitiveness. Therefore, if the pattern shown in FIG. 1A is formed on the reticle 101 by use of the i-line stepper, it becomes necessary to use master masks of a number to cover the entire region.
That is, in the pattern shown in FIG. 1A, the number of master masks in the X direction is five since 99.5 mm/21 mm=4.7 and the number of master masks in the Y direction is six since 120.5 mm/21 mm=5.7.
Therefore, as shown in FIG. 1B, it is necessary to use 5×6=30 master masks 103 (103-1 to 103-30).
Thus, in the conventional method which forms master masks used to draw a pattern larger than the shot on the reticle 101, the number of master masks 103 cannot be reduced even if the functional elements A having the repetitiveness are present in the pattern since the pattern of the dicing region 102 has no repetitiveness. The cost for forming the master masks directly gives influence on the price of a reticle to be formed by use of the master masks, that is, the manufacturing cost thereof. Therefore, in order to lower the cost of the reticle and the cost of a semiconductor product having a circuit pattern formed by use of the reticle, it is necessary to reduce the number of master masks.